Every time people come up with stuff like this I'm always confused, because we all know in the end that people end up resembling the charts based on their birth times. Not only that, but good luck with pinpointing the moment of conception because, to be blunt about it, it could happen at any time after ejaculation. Fertilization isn't always immediate. It would literally be impossible for anybody to get a precise chart based on something like that in the first place. The closest you could get, if you were lucky, is probably a general day, but how many people do you know of, write down every time they have sex? Good luck with that theory.
Besides, people's natal charts based on their actual time of birth tend to have similar placements and aspects to their parents ANYway. Astrological things are inherited just like physical traits are, you don't need to go back and figure out when something got stuck in somewhere for that.
My SN and ascendant are in the same sign as my mother's sun. I also inherited a few aspects from her, like Sun-Neptune. I'm pretty sure my Mars is in the same sign as my dad's sun; and my mother's DNA asteroid forms an exact conjunction to my Venus. That's not even the half of it; if I took the time to rattle off all the shared signs, aspects, and chart elements I'd be here all day.
I took the time to look at a few of my siblings charts too, and it's the same thing. Parents pass on their astrological data to their kids. That shows up in the natal chart based on birth time. You don't need a conception chart for that.